PUBLIC HEALTH ASSESSMENT
NAVAL AIR STATION CECIL FIELD
(a/k/a USN AIR STATION CECIL FIELD)
JACKSONVILLE, DUVAL COUNTY, FLORIDA
Naval Air Station (NAS) Cecil Field is approximately 14 miles southwest of Jacksonville innortheastern Florida. NAS Cecil Field was in operation (except for brief periods of inoperation)from 1941 to September 30, 1999 when operations ceased. The base property occupied more than31,000 acres, primarily in Duval County with the southern portion of the base extending into ClayCounty. Approximately 17,200 acres will be transferred to the private sector (non-military) andthe remainder will be transferred to NAS Jacksonville. The future ownership of these areas willbe the city of Jacksonville (10,560 acres), the Jacksonville Port Authority (6,000 acres), and ClayCounty (641 acres). To date, more than 95% of the property designated for the private sector use has been transferred.
Historically the mission of the base had been to provide facilities, services, and material supportfor the operation and maintenance of naval weapons and aircraft. NAS Cecil Field was listed onthe U.S. Environmental Protection Agency (EPA) National Priorities List (Superfund List) in1989, based on indications that there was shallow groundwater, surface water, and soilscontamination. Twelve "operable units" consisting of twenty-four separate areas of contaminationhave been identified as well as other potential sources of contamination. Environmentalinvestigations at NAS Cecil Field are in varying stages of completion. Less than 800 acres of the17,200 acres have been determined to be contaminated and require additional investigation orremediation. The majority of contaminated sites are located on the Main Base primarily to thewest of the north-south runways.
ATSDR has focused our review of environmental exposures primarily on future uses of theproperty and has strived to provide information on safely managing the remaining environmentalhazards for the current and future property users. Those situations we believe need more carefulfuture management are the main focus of this document. From our review, ATSDR identified ninesituations which have the most potential for human exposure. One of the situations poses a healthhazard, four require more data or information about whether contamination has reached areaswhere people are living or working, three others could have exposure occurring, but exposure tothe contaminants at the levels detected would not pose a health hazard, and one currently posingno public health hazard. The areas or activities people engage in that could result in exposure areas follows:
- Future building occupants could be exposed to fuel components and other volatilecompounds seeping into indoor air from on base groundwater contamination.(Future -Indeterminate Public Health Hazard, Current - No Public Health Hazard)
- In the future, building occupants could be exposed to contaminated drinking water onbase. (Future - Indeterminate Public Health Hazard, Current - No Public Health Hazard)
EPA and the Navy should consider implementing an assessment of new or restructuredbuildings at risk for indoor air contamination as part of the Superfund ComprehensiveFive Year Review.
EPA and the Navy should consider implementing an assessment of new and existing wellsat risk for contamination as part of the Superfund Comprehensive Five Year Review.
Jet Fuel Pipeline (between NAS Cecil Field and NAS Jacksonville along 103rd Street)
- Off-base private drinking water wells near the areas with past pipeline leaks and other pollution sources in the vicinity could be or become contaminated. (Indeterminate Public Health Hazard)
- Current and future building occupants living near the 103rd Street Jet Fuel Pipeline couldbe exposed to fuel components and other pollutants seeping into indoor air. (Indeterminate Public Health Hazard)
The Florida Department of Environmental Protection (FDEP) should provide educationalmaterial (such as radio or television broadcast or printed material in the newspaper)warning well owners of the possible regional contamination hazards prompting them tohave their well sampled annually. Alternatively, a complete well survey can be conductedand people notified individually.
Because individual private, and especially shallow, wells can be affected by fuel leaks,improperly functioning septic tanks, small industrial waste disposal practices, andresidential use and disposal of pesticides along 103rd Street, people should have their wellstested for volatile organic compounds, semi-volatile organic compounds, pesticides, andmetals.
Building occupants should report fuel odors in indoor air to the FDEP, Bureau ofEmergency Response 1-800 320-0519 or (904) 807-3300 or the local fire department.
Site 15 (Blue Ordnance 10)
- If unremediated or remediation is limited, current trespassers and future recreational userscould be exposed to lead and other contaminants in soils, sediment, surface water andpossibly other firing ranges on the Yellow Water Weapons Area. (Future-IndeterminatePublic Health Hazard, Current - No Apparent Public Health Hazard)
- People could be eating contaminated fish or turtles from Yellow Water or Sal TaylorCreek draining Site 15; however, the levels are predicted to be too low to pose a publichealth hazard. (Current - No Apparent Public Health Hazard)
The Navy, FDEP, and EPA are working to prevent people from having frequent contactwith soils by implementing deed restrictions, monitoring during the SuperfundComprehensive Five Year Review, and possibly conducting limited soil removal. ATSDRrecommends continuing evaluation of the land use controls during the SuperfundComprehensive Five Year Review to determine if changes in the economy or the regionalvision for NAS Cecil Field redevelopment result in a proposed residential reuse orrecreational activities where children could have frequent (i.e., several times a week)contact with the soils.
High dissolved lead levels have been found in surface water samples that run off Site 15and during heavy rain events, possibly into Yellow Water Creek. We are recommendingthat the Superfund Comprehensive Five Year Review include an evaluation of whetherincreased use of this area is resulting in more frequent harvesting of fish and turtles,especially if Site 15 soils are left unremediated. Additionally, ATSDR's review of theNavy's shallow groundwater data shows that there are some contaminants (e.g., antimonyand lead) in the groundwater at Site 15 that could exceed the drinking water standards. Therefore, we are also recommending that the groundwater use situation be part of theSuperfund Comprehensive Five Year Review.
Lead and Asbestos in Base Housing
- Current and future building occupants and visitors, particularly children, could be exposedto lead-based paint, lead in tap water, and asbestos insulation found in many buildings onbase. Those hazards are indeterminate because the hazard management (preventing paintchipping, flushing water lines, covering insulation) efficacy is unknown.(Indeterminate Public Health Hazard)
The Navy or the redevelopment authority should provide information to new residents,developers, and tenants not only on the location of the lead paint and asbestos inbuildings, but on how to manage those hazards. The Navy should determine if the leadsolder is leaching into the drinking water at levels of health concern. If so, they shouldeither remove the lead hazard or provide information to new occupants on tap waterflushing techniques.
Eating Fish and Turtles from On-Base Lakes and Creeks
- In the past, fish in Lake Fretwell were contaminated. New lakes or enlargement of existinglakes may inadvertently bring contamination to the water bodies from nearby remainingcontaminant source areas and therefore, warrant periodic reassessment. (Current - NoApparent Public Health Hazard)
ATSDR recommends that a review of the potential for fish and turtles to becomecontaminated in the future be investigated as part of the Superfund Comprehensive FiveYear Review.
Unexploded Ordnance (UXO)
- UXO could be a future explosion hazard for people digging or excavating near many areas on the Main Base and on the Yellow Water Weapons Area. (Public Health Hazard)
UXO surveying and clearing has been done at a majority of the high risk areas on base.Although the likelihood is extremely low that people could be injured or killed by UXO, apotential current and future hazard still exists and cannot be entirely eliminated.Additionally, the Navy also used at least four off- base areas during the WWII era forbombing ranges. These areas have been identified by the Army as formerly used defensesites. The Navy should coordinate with the Army Corps of Engineers and new tenants toensure the proper program provides public education on the locations and hazardsassociated with disturbing UXO. Institutional controls (i.e., no digging) may be needed insome areas. The Navy should verify emergency phone numbers and reporting informationand provide clearing and reporting procedures to residents, bombing range owners,developers, utility contractors, and municipalities before people dig or excavate in UXOlocations.
This public health assessment (PHA) evaluates NAS Cecil Field and the properties previouslypart of NAS Cecil Field before Naval operations ceased. In response to the NPL listing, theAgency for Toxic Substances and Disease Registry (ATSDR) conducted this public healthassessment by reviewing environmental data and reports and visiting NAS Cecil Field in January29-30, 1991, February 17- 21, May 27 - 28, 1997, October 19-20, 1998, and October 24-25, 2000.NAS Cecil Field is a base closure site with some information available as to proposed reuse. Wehave focused our review primarily on future uses and strived to provide information on safelymanaging the remaining environmental hazards for the current and future property users. Thosesituations we believe need more careful future management are the main focus of this document. We include our review of all of the environmental contamination areas on base in Appendix A.
Naval Air Station Cecil Field (NAS Cecil Field) is located approximately 14 miles southwest ofJacksonville in northeastern Florida (U.S. Navy, 1997a). (Figure 1). When operational, the baseproperty occupied over 31,000 acres, primarily in Duval County. The southern portion of the baseextended into Clay County (U.S. Navy, 1997b).
Prior to development as a naval air station, the surrounding properties were undeveloped ruralfarm lands (U.S. Navy, 1997b; Arthur Andersen LLP, 1996). Today, the station is bordered on thesoutheast, northeast and northwest by low-density residential and agricultural properties. The landsouthwest of the base is mostly agricultural (tree-farming) with limited residential development.Some retail and commercial development exists along 103rd Street, east and west of the base(Arthur Andersen LLP, 1996). Additional information on the demographic makeup of the baseand the surrounding community is provided in Figure 2.
Historically the mission of the base has been to provide facilities, services, and material supportfor the operation and maintenance of naval weapons and aircraft. The operations conducted insupport of this mission included: operation of fuel and oil storage and disposal facilities; aircraftmaintenance, aircraft engine repair and turbo-jet test cells; fire training; target ranges; and specialweapons storage and support (U.S. Navy. 1997a, 1997b). Shallow groundwater, surface water,and soils have become contaminated from past waste disposal practices and accidental spills ofchemicals, resulting in NAS Cecil Field being placed on the National Priorities List (NPL) forhazardous waste site investigation and clean-up.
NAS Cecil Field is working with the U.S. Environmental Protection Agency (EPA) and theFlorida Department of Environmental Protection (FDEP) to characterize the environmentalcontamination and clean-up those areas which pose a hazard to public health and theenvironment. The primary environmental contaminants at the base include heavy metals, jet fuelsand oils, and volatile organic compounds (solvents) (U.S. Navy, 1997a). Less than 800 acres ofthe 17,200 acres of the base have been determined to be contaminated and require additionalinvestigation or remediation (U.S. Navy, 1997b). Therefore, they are not yet suitable for transfer(U.S. Navy, 2001a). The majority of contaminated sites are located on the Main Base primarily tothe west of the north-south runways (Figure 3). A summary of ATSDR's public health evaluationof these sites is provided in Appendix A. For detailed information on the Navy's continuedenvironmental investigation and remediation plans at NAS Cecil Field, refer to NAS Cecil Field's documents at the public repositories:
Cecil Field NAS Repository
Jacksonville Public Library
122 N. Ocean Street
Jacksonville, FL 32202
Westbrook Branch Library
2809 Commonwealth Ave.
Jacksonville, FL 32254
NAS Cecil Field had been in operation from 1941 until 1999. In July 1993, the Base Realignmentand Closure (BRAC) Commission recommended the closure of NAS Cecil Field. The station'saircraft, equipment, and personnel were relocated to other Navy facilities. Naval operations atNAS Cecil Field ceased September 30, 1999.
As part of the closure activities, the majority of the Main Station and the Yellow Water WeaponsArea properties have been returned to the Jacksonville community for redevelopment (U.S. Navy2001a). The Cecil Field Development Commission has been established by the mayor ofJacksonville to oversee the base conversion process and develop a reuse plan for the base.Outlying Landing Field (OLF) Whitehouse, the Land Target Complex, the 252 acre Yellow WaterFamily Housing west of the Yellow Water Weapons Area, and the additional outlying parcelshave been retained by the Navy (Arthur Andersen LLP, 1996) (U.S. Navy 2001a).
NAS Cecil Field land holdings to be turned over for redevelopment include the following: (i)Main Station (8,500 acres); (ii) Yellow Water Weapons Area (7,900 acres); and (iii) JacksonvilleHeights (800 acres). Other areas that were once part of NAS Cecil Field include the (iv)(OLFWhitehouse (2,565 acres), located 7 miles north of the Main Station; (v) Pinecastle Land TargetComplex (11,142 acres leased from US. Forest Service), located 90 miles south of Jacksonville;and (vi) additional outlying parcels comprising 52 acres of over-water training areas andtransmitting towers (U.S. Navy, 1997b).
Approximately 17,200 acres will be transferred to the private sector (non-military) heavyindustrial - 1,030 acres, light industrial - 3,400 acres, residential/light office - 220 acres,commercial - 300 acres, parks - 2,260 acres, conservation - 3,990 acres, aviation-related facilities- 6,000 acres. The future ownership will be city of Jacksonville - 10,560 acres, Jacksonville PortAuthority - 6,000 acres, Clay County - 641 acres (City of Jacksonville, 2000). Figure 4 shows theProposed Base Reuse Map (City of Jacksonville, 2000).
Twelve Operable Units (OUs) consisting of twenty-four separate sites have been identified aswell as numerous potential sources of contamination. Investigations at NAS Cecil Field are invarying stages of completion. Clean-up actions include long term monitoring of creek sedimentsand surface water, natural attenuation, soil excavation with off-site disposal and air sparging ofgroundwater. The various remedial activities at NAS Cecil Field have and will addressgroundwater plumes of chlorinated solvents and petroleum waste products, as well as surface soils, sediments and sources contaminated with metals and organics (EPA, 2000).
ATSDR visited Naval Air Station Cecil Field on January 29-30, 1991, February 17- 21, May 27 -28, 1997, October 19-20, 1998, and October 24-25, 2000. The purpose of the visits was to collectthe information needed to identify any public health issues related to exposure to environmentalcontamination in the soil, water, air, and buildings at the base and to identify community healthconcerns.
During our tour of the site to observe the environmental conditions at the base, we met with Navypersonnel and representatives from the federal and state agencies. Our discussions addressed thenature and extent of chemical contamination at NAS Cecil Field, the proximity of chemicallycontaminated areas to on- and off-base populations, and the types of human activities that couldlead to exposures to the contamination. In addition, ATSDR attended the February, 1997, jointmeeting of the NAS Cecil Field, NAS Jacksonville, and Naval Station Mayport RestorationAdvisory Boards and the October 1998 and 2000 RAB meetings. The information collectedduring our site visits and discussions has been integrated with our review of environmentalsampling data to draw the conclusions about public health issues at NAS Cecil Field that are presented in this public health assessment document.
In preparing this public health assessment, ATSDR relied on information provided in thereferenced documents and contacts. The agency assumes quality assurance and control measureswere followed with regard to chain of custody, laboratory procedures, and data reporting. Thevalidity of analyses and conclusions drawn in this document is determined by the reliability of theinformation referenced in this report.
For all sites on the Main Base and Yellow Water Weapons Area, numerous chemicals in manycontaminated media (groundwater, soil unspecified depth, sediment, surface water, biota (fish andworms) provided in electronic format to ATSDR have unspecified locations. Additionally,applicable sample data were identified for the electronic format and certain data sets collectedearly in the program were not entered. Therefore, a number of locations named in the electronicreport cannot be cross referenced to hard-copy reports provided to ATSDR. The Navy did notintend the electronic system to be a "stand alone" system, but it may be confusing to people,especially new property owners or developers, who may think they are looking at the total set ofdata with the electronic system when they are not.
ATSDR has also identified data gaps, data format and data presentation limitations in hard copyresults that will limit the information that can be provided to future users of the data.
ATSDR reviewed the environmental data generated from investigations at NAS Cecil Field to determine if there are any associated past, current and future public health hazards. See Appendix B for information on how ATSDR assesses exposure. From this review, ATSDR identified nine situations which have the potential for human exposure. One of the situations poses a health hazard, four require more data or information about whether contamination has reached areas where people are living or working, three others could have exposure occurring, but exposure to the contaminants at the levels detected would not pose a health hazard, and one currently posing no public health hazard. These nine exposure situations are discussed in the following sections. They are organized by areas or by activities people engage in that could result in exposure and are as follows:
OUTLINE OF THE NINE POSSIBLE EXPOSURE SITUATIONS
A. On-Base Groundwater
B. Jet Fuel Pipeline (between NAS Cecil Field and NAS Jacksonville)
C. Site 15 (Blue Ordnance 10)
D. Lead and Asbestos in Base Housing
E. Eating Fish and Turtles from On-Base Lakes and Creeks
F. Unexploded Ordnance
Past use, disposal, and accidental spills ofhazardous substances on base havecontaminated the groundwater in at least 23 on-base areas. In several areas, highlyconcentrated groundwater contamination isclose to the ground surface beneath buildings onbase. ATSDR is concerned that water, sewer,and other utility lines coming into the buildingswould provide a channel increasing thepossibility of contaminant migration fromgroundwater into indoor air. Because many ofthe contaminants are highly volatile, they couldreadily seep into the buildings, possibly makingthe air indoors unsafe to breathe. Based onATSDR recommendations, the Navy determinedthe current buildings most susceptible togroundwater contaminants migrating intoindoor air. Those buildings were determined notto be at risk because they were buildings withconstant air exchange such as open airplanehangers. However, future new or restructuredbuildings could still be at risk, but simpleprecautions could greatly reduce that risk.
Drinking water for the base is supplied by deepwells. Several deep wells are near areas wherecontamination has been detected in the shallowaquifer. Old well casings could provide an easymechanism for contaminants to travel fromshallow to deeper aquifers. Although notcurrently contaminated, deep wells with oldcasings could become contaminated in the futureif the shallow contaminated groundwater is notprevented from seeping into the deeper aquifer.ATSDR recommends that the new well owners improve the wellhead protection program andmaximize the use of monitoring data to reduce the risk.
Background and Land Use
Some of the operations conducted in support of this mission that may have contributed togroundwater contamination included operation of fuel and oil storage and disposal facilities,aircraft maintenance, aircraft engine repair and turbo-jet test cells, fire training; target ranges,special weapons storage and support. Contaminants that possibly spilled or leaked into thegroundwater include: volatile organic compounds, chlorinated hydrocarbons, aromatichydrocarbons (benzene, toluene, ethylbenzene, and xylene (BTEX)), paraffin hydrocarbons,mercury, and fuel additives.
Cecil Field Known Areas of Groundwater Contamination
Plumes have been identified and monitoring is ongoing. Restrictions on future use of shallow contaminated groundwater are planned or a deed restriction is required by the Record of Decision. There are approximately 23 areas identified to date with groundwater contamination including the following:
Installation Restoration (IR) Sites with Groundwater Contamination:
Underground Storage Tank (UST) Sites with Groundwater Contamination:
ATSDR evaluated the likelihood of people to be affected by contaminated groundwater caused by the base's past use, disposal, and accidental spills of hazardous substances in at least 23 different areas on base (Figure 5).
We identified two possible situations in which people could be exposed to groundwatercontaminants: (1) people using on-base buildings over groundwater contamination, and (2) peopleusing the base wells or installing new wells in the future.
- People Using On-base Buildings Over Groundwater Contamination - Potential Migration to Indoor Air
During its operation, NAS Cecil Field had a large number and quantity of fuel and othercontaminant releases due to past waste disposal practices and accidental spills. Appendix C shows the large quantity of fuels (only) spilled over the years of operation.
To remedy the groundwater contamination, the Navy has installed treatment systems in areas withthe highest concentrations. Those systems have been effective in reducing the contaminantconcentrations in groundwater. For example, the groundwater monitoring wells near the Building313 source area showed concentrations of trichloroethylene (TCE) as high as 410,000 parts perbillion (ppb) in 1998 rising to over 700,000 ppb in 1999 (Tetra Tech, 2000). After startup of theAir Sparging/Soil Vapor Extraction (AS/SVE) system in June 1999, the highest groundwaterconcentrations quickly dropped below 1,000 ppb and the system has been operating in pulsemode since May 2000 to maintain the source area contamination below the 1,000 ppb source areacleanup goal concentration (U.S. Navy, 2001a).
Although the groundwater contaminant concentrations have been reduced, they remain high enough for the contaminants to migrate into indoor air. Elevated contaminant concentrations combined with other characteristics such as depth to groundwater, groundwater movement, and building attributes, greatly increase the likelihood for volatile organic compounds to migrate from groundwater into indoor air of buildings located above contaminant plumes. Some of the groundwater contaminants have the potential to migrate into the building's indoor air due to their volatility. Additionally, the 23 groundwater contamination areas have contamination in the surficial aquifer. In general, the surficial groundwater at NAS Cecil Field is at a depth of 0 to 50 or 100 feet and primarily discharges to local lakes and creeks on the Main Base area. Water is recharged locally in the Yellow Water Weapons Area and flows from the groundwater to the lakes and creeks on the Main Base area. The upward groundwater movement of the recharge effect that flows into lakes and creeks slows the downward push of contaminants to deeper aquifers (Hillford, 1996) allowing contaminants to stay at the groundwater surface close to the soil interface.
In addition to the groundwater attributes (e.g., shallow, concentrated), the building characteristicscan also contribute to the groundwater off-gassing into the buildings. Soil gas can diffuse directlythough the various openings that penetrate the foundation through cracks, gaps, footers, basementwalls and walls below grade level, and poor seals around utility entry points. The action ofmechanical ventilation, exhaust fans, and ventilation systems may increase air exchange and alsoincrease soil gas movement (migration) into the building.
The number of small closed rooms create pockets where gases can accumulate, confined spacesespecially below grade, and closed windows, running air conditioning, lowers the air exchangerate allowing increased build up of gas concentrations. Contaminated groundwater seeping intothe building or draining into a sump may also release gases.
In the public comment version of this public health assessment, ATSDR considered thegroundwater attributes and building characteristics and determined that groundwater could be off-gassing into the buildings. We recommended that indoor air safety should be confirmed.
In response, the Navy determined the locations with the greatest potential for indoor aircontaminant migration. The analysis showed 55 locations across the facility had the greatestpotential for indoor air migration. The Navy evaluated all locations within 100 feet of a building;that resulted in 18 locations. In all cases, the Navy decided on " no further action" because thebuildings either no longer existed or the current use of the building has constant air exchange(e.g., open airplane hangers). The Navy concluded that any future development of thecontaminated area will require design to prevent indoor air contamination due to underlyingcontamination. Appendix D shows the Navy's evaluation.
Given the right conditions, new or restructured buildings in at least the 55 locations evaluated inAppendix E could be at risk for indoor air contamination. The Navy notifies new property ownersof existing groundwater contamination by way of the Findings of Suitability to Transfer (FOST)document. However, the hazards of building on top of contaminated groundwater are notoutlined. The redevelopment authority should distribute educational material to developersinforming them of possible indoor air contaminant hazards when building over the contaminatedgroundwater areas. Developers should consider installing vapor barriers when building in areaswith shallow groundwater contamination. Developers should also consider sampling indoor air innew buildings. That sampling should include biogenic gasses (e.g., methane, ethane, etc),chlorinated hydrocarbons (e.g., TCE, TCA, etc), and hydrocarbons (e.g., benzene, ethylbenzene,etc). EPA and the Navy should consider implementing an assessment of new or restructuredbuildings at risk for indoor air contamination as part of the Superfund Comprehensive Five Year Review.
Appendix E provides information on Strategies for Indoor Air Sampling for those considering future use of enclosed buildings over contaminated groundwater areas.
- People Using the Base Wells or Installing New Wells in the Future.- Potential Migration to Drinking Water Wells
There remain a number of base drinking water wells in use that draw water from the deepergroundwater aquifer. Several wells are near areas of surficial groundwater contaminationalthough the Navy reports that the wells are hydrologically upgradient from contamination.Figures 5a and 5b show the groundwater contamination locations and current supply wells.
The drinking water system is being turned over to the city of Jacksonville. If the city chooses touse the existing supply wells, they could still be at risk even though the Navy predicts that thecurrent supply wells are upgradient from the groundwater contamination areas. The risk comesfrom the old (1940s) well casings that could breakdown and carry contamination into the drinkingwater zone. Even though the groundwater flow in the shallow aquifer appears to naturally flowaway from the existing wells, if enough pumping takes place, groundwater can be pulled toward awell even when it is naturally flowing in the opposite direction, especially if the well casing iscompromised. Future well head protection programs should include monitoring the integrity ofthe 1940 well construction materials including grout, and corrosion control of the casings.
The city of Jacksonville's Jacksonville Electric Authority (JEA) has indicated that they plan toclose all existing potable wells on the Cecil Commerce Center (CCC) and build new ones exceptfor those on Jacksonville Port Authority (JPA) property which will be used for fire fighting.Because of the remaining groundwater contamination, routine sampling of new or existing wellsis prudent. This should be performed by the system operators. Routine drinking water sampling(possibly every three years) should be done on any systems fed by wells on base. New wellinstallation should be restricted without wellhead protection, corrosion resistant casings, aquiferprotection during drilling, and if needed, water treatment.
Notification of the groundwater hazards, including the location of contamination horizontally andvertically (3-dimensional presentation), should also be given to developers and be on file withthe city and county.
Future sampling should consider additives. Aviation gasoline (Avgas) continues to containsignificant concentrations of alkyl lead, typically at levels greater than 1,000 ppm. Icing inhibitor,antioxidant, corrosion inhibitor, metal deactivator, static dissipater, anti-oxidants, biocides,conductivity additives, detergent additives, oxygenates including methyl tertiary butyl ether(MTBE), and thermal stability additives were in JP-5, Mogas, Avgas, and other historical usedfuels (AFCEE, 1999). Appendix F lists common fuel additives for jet fuels and provides more detail on their use.
Table 1 outlines the possible exposure situations from contaminated groundwater.
PUBLIC HEALTH ACTION PLAN - GROUNDWATER CONTAMINATION ON BASE
People using on-base buildings over or near the areas with surficial groundwater contamination.
People using the base wells or installing new wells in the future.
Use of On-base Groundwater
The 103rd Street pipeline is an 8" diameter pipeline that extends 15 miles from NAS Jacksonville to NAS Cecil Field underneath Roosevelt, Timaquana, and 103rd Streets. The pipeline is currently out of service and was emptied, cleaned, and abandoned in place. Although no catastrophic leaks have been reported, it is possible that an undetermined amount of jet fuel leaked from the pipeline (at on- and off-base locations) for some period of time during the pipelines 43 year operation. A 1994 investigation of the pipeline required several of the previously identified 81 anomalies to be excavated and the section of pipe checked for its integrity (repaired or replaced). The amount and extent of soil and groundwater contamination at the repaired locations has not been investigated. In a supplemental investigation in 1999, the Navy determined that new anomalies investigated did not have significant soil or groundwater contamination. However the 1994 repairs were not re-investigated.
Additionally, many other businesses (e.g., gas stations, etc.)are or were along this 15-mile stretch that have contributedto soil and groundwater contamination. According to EPAreports, there are as many as 25 other current chemical orfuel hazard sources along the pipeline and an unknownnumber of past sources. The extent of groundwatercontamination and private well use in this area is not wellcharacterized; therefore, the extent of the hazard is unknown.This is a heavily populated area where water, sewer, andother utility lines could move the local contamination furtherfrom those sources.
Because of the variety and number of contamination sourcesin this area, there is enough risk to advise people usingprivate wells for drinking water and bathing to test theirwater annually for volatile organic compounds, semi-volatileorganic compounds, pesticides, and metals. Since thecontaminants could also move into indoor air, people shouldreport strong odors to the fire department for investigation.
Historically, NAS Cecil Field received approximately 200,000 gallons of jet fuel each daythrough an eight-inch diameter underground pipeline which extends from the NAS Jacksonvilletank farm to NAS Cecil Field North Fuel Farm (NAS Cecil Field, 1997b). Put into service in1954, the pipeline has been used to transport both JP-4 and JP-5 type aviation fuel for 15 milesalong, and almost entirely underneath, Roosevelt, Timaquana, and 103rd Streets in the city ofJacksonville (Figure 6) (Delaney, 1996; ABB-ES, 1995a). The pipeline also passes throughseveral wetland areas. The pipeline is buried at depths from 2 to 15 feet. The shallow water tableranges from 2 to 6 feet deep.
There are no reported catastrophic releases from the pipeline in its 43-year use. However,beginning in 1989, releases from the pipeline were discovered. As a result, in 1990, the Navybegan conducting corrosion surveys. Even small leaks from this high volume pipeline (estimatedto have transported 200,000 gallons per day more than 43 years) could have resulted inthousands of gallons of fuel lost. Those fuel leaks, compounded with leaks from undergroundstorage tanks from abandoned service stations and other possible hazardous substance releasesalong Roosevelt, Timaquana, and 103rd Street, put private well users at greatest risk. The pipelineis currently out of service and was emptied, cleaned and abandoned in place starting in 1997.
Additionally, there are reportedly as many as 25 other current chemical or fuel hazard sourcesalong the pipeline and an unknown number of past sources.
Land uses adjacent to the pipeline path are residential, commercial, and light industrial. Privateand public wells are reportedly used in the area, although to what extent, we were not able todetermine. Some reports indicate that 25 private wells are within a one quarter mile radius ofNAS Cecil Field (Jamel, 1990).
Exposure Evaluation and Public Health Implications
We discuss here the documented releases, results of the corrosion surveys, and possible exposuresituations.
Documented Releases from the Pipeline
Release from the 103rd Street Jet Fuel Line, Kerr/McGee, and Texaco properties
In 1989, a release of JP-5 jet fuel from the pipeline was discovered to be co-mingled withpetroleum (gasoline) releases from adjacent sources, including the Kerr-McGee and Texacoretail fuel properties (Jamel, 1990; Professional Service Industries, 1991). Shallow ground waterand soil at this spill area were contaminated with benzene, toluene, ethylbenzene, xylenes,methyl-terbutyl ethylene, naphthalenes, and lead (Jamel, 1990; Professional Service Industries,1991; Bechtel,1996). No water wells were located on these properties. Gross contamination ofthe soils and groundwater was remediated in 1996 through free product recovery and soilremoval. Migration and degradation of the groundwater contamination is currently beingmonitored (Lancaster, 1997; NAS Jacksonville, Public Works files, 1997).
The petroleum contamination extended underneath an adjacent residence on 103rd Street. Duringthe course of the investigation, from 1989 through 1996, the family continued to live in theirhome. Repeated rounds of sampling over an eight-year period demonstrated that the well watersupply for the residence was never impacted by the shallow groundwater contamination (NASJacksonville, Public Works files, 1997). The residential property was ultimately purchased in1996 by the Navy in support of soil and groundwater clean up activities (Bechtel, 1996).
Under circumstances of shallow groundwater contamination, volatile chemicals may migratethrough soils and into homes through the backfill material along utility service lines entering thehome and through cracks in building foundations. Indoor air sampling was not performed at theresidence on 103rd Street to determine if gas migration from the shallow groundwatercontamination was entering the home; therefore, no conclusions can be drawn regarding whetherthe indoor air quality was impacted. No complaints of indoor air odors were expressed by theresidents to the Navy (Lancaster, 1997).
103rd Street and "A" Avenue spill site, 1997
In July 1997, stressed vegetation was noted near the intersection of 103rd Street and Avenue "A"on base. Sampling results, pipeline repair, and clean up work indicated that approximately 6,000gallons of jet fuel had been released to soils and shallow groundwater from a 1/16 -1/8 inchdiameter hole in the pipeline. All soil within 30 feet of the pipeline leak was excavated down to adepth of one foot below the surface of the groundwater. The soil was treated and disposed off-site and the excavation was backfilled. Monitoring wells were installed at the site of the releaseto assess the extent of groundwater contamination and to determine if additional remediation wasneeded (NAS Cecil Field, 1997b).
In response to the 1997 leak at "A" Avenue, the Navy Defense Fuels Supply Commanddetermined that the pipeline should be put on stand-by status. The pipeline was removed fromservice in September 1997 and the base received fuel by truck transport on a daily basis (TetraTech, 1999a).
Pipeline Inspections, Other Soil Excavations, and Pipeline Closure
Four corrosion surveys have been performed on the pipeline; in 1990, 1994, 1996, and 1999.Corrosion surveys estimate pipe wall thickness; areas where the wall thickness appears to bebelow a minimally required thickness are termed "anomalies". Anomalies represent areas wherepipeline leaks may be occurring, or may occur in the future.
A 1990 corrosion survey identified 90 anomalies (PM&A, 1992). Excavations were performed in four areas suggested by the 1990 survey: Bent Creek, the Go Cart Track, an additional home on 103rd Street, and one location at NAS Cecil Field. The only leak found was the one adjacent to the residence at 103rd Street. In September 1990, the Navy performed soil borings at several suspected anomaly locations along the pipeline to determine if there were any additional fuel releases; no releases were found (Delaney, 1996).
A 1994 corrosion survey identified 23 anomalies (ABB-ES, 1995a). In 1994, a pipe integrityinvestigation was conducted and 81 thickness anomalies were discovered along the pipeline.According to recent information from the Navy, based on conversations with former NavyPublic Works Center personnel, some areas of potential concern (called "anomalies") wereinvestigated in order to verify the accuracy of the instrumentation used to inspect the pipelinethickness. The Public Works Center personnel did not identify soil or groundwatercontamination when excavating these areas in order to cut the pipe to confirm its thickness. (U.S.Navy, 2001a).
In 1996 another survey was conducted that identified 19 principal anomalies and 13 of theapproximately 15 original valves (Tetra Tech, 1999a).
In July 1997 a leak was detected in the pipeline 1/4 mile from gate A of NAS Cecil Field. Aninvestigation was ongoing in 1999 (Tetra Tech, 1999a). An air sparging/soil vapor extractionsystem at Avenue "A" was placed in operation in May 2000 (RAB Site update, 2000).
From the work conducted based on the 1999 work plan for investigation, the Navy identified 32principal anomalies and valves (this included the 19 discovered in 1996) along and under the 15miles of road between NAS Cecil Field and NAS Jacksonville (Tetra Tech, 1999a). The Navycompleted the investigation of the anomalies and valves along the pipeline in March 2000. Thework (Tetra Tech, 1999a) included an average of four soil borings at each of the 32 locationsidentified to have anomalies. Groundwater sampling of each of the soil borings was conductedfor boring below the water table. Permanent groundwater monitoring wells were installed atlocations in which contamination was identified from soil and groundwater sampling. Soil gasevaluation using a Photoionization Detector of unsaturated soils (vadose soils) was performedfor borings above the water table. Methane was assumed to be present, but was not sampled(Tetra Tech, 1999a). From this investigation, the Navy determined that limited soil andgroundwater contamination was present from the 32 anomalies and 13 valve locations. However,the repaired locations from 1994 were not re-investigated (Tetra Tech, 1999a).
The jet fuel pipeline was closed, cleaned, and abandoned in place. In-place closure wasnecessary since the pipeline runs underneath the heavily trafficked 103rd Street. The closure andinvestigation activities will be integrated and conducted under the Florida Department ofEnvironmental Protection (FDEP) underground storage tank program.
Possible Exposure Situations
ATSDR evaluated the possible current and future exposure situations at or near the jet fuelpipeline and outlined them in Table 2.
- People using private wells in the vicinity of the jet fuel pipeline and other potential sources along 103rd Street
We were unable to determine the extent of private well use near or along the pipeline. Within aone-quarter mile radius of the NAS Cecil Field, there are 25 private or privately-owned small (producing less than 100,000 gallons per day) public water supply wells (Jamel, 1990).
EPA Enviromapper lists as many as 25 possible sources of environmental pollution along the pipeline (See Figure 7). Past leaks from the pipeline along with contaminants from other sources could contaminate nearby wells, especially shallow wells. The extent of groundwater contamination in this area is not well characterized; therefore, the extent of the hazard is unknown.
- People breathing gases that have migrated from the groundwater and soil contamination into buildings
Although not as likely as the private well water contamination situation, highly concentrated soil or groundwater areas could release volatile gases into buildings and pose a health risk. Since the extent of contamination has not been determined, people should report strong odors to the fire department for investigation.
PUBLIC HEALTH ACTION PLAN - JET FUEL PIPELINE AND OTHER
ACTIONS TAKEN OR PLANNED
Site 15, a former munitions burning area, is slated for redevelopment as a wildlife corridor. Future activities within the corridor could include recreational uses such as horseback riding, biking, and hiking. Lead poses the greatest hazard here as it has been found in soil, sediment, and surface water. The reported median lead level in soil here (at unspecified depths) is 163 ppm, the average is 1,157 ppm, and the maximum level found was 65,500 ppm. Those levels are extremely high and frequent contact with soils (i.e., several time a week) here could present a health hazard for children under six years of age. The Navy, FDEP, and EPA are working to prevent people from having frequent contact with soils by implementing deed restrictions, monitoring during the Superfund Comprehensive Five Year Review, and possibly conducting limited soil removal. ATSDR's concern is that long-term, land use controls are difficult to maintain and it is possible that the area could become residential 50 years from now. We are recommending vigilant followup by all stakeholders on this issue.
High dissolved lead levels (a median of 205 ppb)have been found in surface water samples that runoff Site 15 and during heavy rain events, possiblyinto Yellow Water Creek. We are recommendingthat the Superfund Comprehensive Five YearReview include an evaluation of whetherincreased use of this area is resulting in morefrequent harvesting of fish and turtles, especiallyif Site 15 soils are left unremediated.
Additionally, since unexploded ordnance has alsobeen found at and near Site 15, clearing and reporting procedures need to be in place before peopledig or excavate.
Background and Land Use
Site 15, also known as Blue 10 Ordnance and part of Operable Unit 5, is a 10-acre area locatedin the southwestern part of the Yellow Water Weapons Area (YWWA; Figure 8). During the1940s and 1950s, this area was used as a skeet and trap range (ABB-ES, 1997a). Around 1967and ending in 1977, diesel fuel was used to ignite ordnance in a metal burn tank. After burning,the ash and residual metals were spread on the ground for disposal (ABB-ES, 1994a). The typesof ordnance burned included small arms, flares, rocket ignitors and nitroglycerin-based solidrocket propellent.
Historical ordnance disposal activities have resulted in contamination of the soils, sediment,surface water and groundwater in the area. Contaminants include metals, pesticides, volatile andsemi-volatile organic compounds, and explosive residues (nitroaromatics) (ABB-ES, 1994a).Polyaromatic hydrocarbons (PAHs) and pesticides have been detected in soil samples; however,the levels are not exceedingly high. Short term, infrequent contact should not result in harmfulhealth effects, although exposure to PAHs and pesticides would need to be reevaluated if theland use changes to more active use (e.g., residential). Some of the PAHs may have lowbioavailability potential since they are in skeet and trap clay targets others may be associatedwith munition ash (ATSDRa, 2001). Lead contamination is the major public health hazard due tothe extremely high levels. Therefore, ATSDR's discussion below focuses primarily on leadcontamination.
Additionally, unexploded ordnance (UXO) locations have been identified on the Yellow WaterWeapons Area (YWWA) including Site 15. Other locations with suspect UXO at YWWA areSite 14, PSC 49 (Skeet Range Facility 804 in operation since 1968, and PSC 4, Mobile TargetArea. Those UXOs were left over from the firing range activities and would therefore tend to besmaller, less powerful rounds. (See UXO section for more details).
Access to the YWWA is unrestricted and casual use by community members can occur. Anexisting bike/hike trail and network of roads through the area enhances Site 15's accessibility torecreational users of the YWWA. The site is posted with signs alerting recreational users of theYWWA roads and trails to the chemical hazards in this area. Runoff from the site is drained bythe Yellow Water River, which flows on-base near the boundary of the YWWA and the YellowWater military housing area (ABB-ES, 1997a). The boundary of the YWWA is fenced betweenSite 15 and the housing area, preventing children from directly accessing the contaminated areafrom the housing complex. Yellow River exits the base and continues to flow south acrossNormandy Boulevard and drains into Sal Taylor Creek. Yellow Water and Sal Taylor Creek areclassified as Class III water bodies allowing use for recreation, propagation, and maintenance offish and wildlife populations. Therefore, fishing could be taking place in those creeks.
Exposure Evaluation and Public Health Implications
ATSDR evaluated the possible current and future exposure situations at or near Site 15. They areoutlined in Table 3; our evaluation conclusions follow.
|Exposure Situation||Activity||Time Frame||People Exposed?||Hazard Category|
|1.People contacting on-site soil, dust, creeks, groundwater, and unexploded ordnance||Trespassing||Current||Yes||No Apparent Public Health Hazard|
|Recreational activities||Future||Possible||Indeterminate (Potential) - missing cleanup and use information|
|2. People who eat fish or turtles from Yellow Water or Sal Taylor Creek draining Site 15||Eating fish or turtles||Current||Unconfirmed||Current - No Apparent Public Health Hazard|
|3. People disturbing UXO * See UXO section of document|
- People contacting on-site soil, dust, creeks, groundwater, and unexploded ordnance
The only current potential exposure situation at Site 15 is by way of trespassing. ATSDRassumes that there is a minimum amount of trespassing since the boundary of the YWWA isfenced between Site 15 and the housing area, preventing children from directly accessing thecontaminated area from the housing complex.
To reduce the hazard more, the Navy has posted signs on paths leading onto the site. The signsstate, "Warning No Trespassing, Contaminated Area Avoid Contact with Soil and Water" andprovide a phone number for additional information. ATSDR recommended and the Navyprovided residents of the nearby housing area, educational material on the need to stay out ofSite 15 until it is cleaned up. Additionally, the Navy increased the number of sign postingsaround Site 15.
ATSDR also assumes that there is limited contact with the most contaminated soils since amajority of the area is covered by vegetation or some other material. The Navy reports that there is up to six inches of leaves and pine needles covering the contaminated lead soils. This also,reduces the likelihood of dust generation, thus reducing the potential exposure to lead.
Source Areas of the Lead
The primary site-related source areasidentified in Navy documents include:(1) lead dust, metallic lead andcorroded lead from the sheet and traprange (shooting positions, targets,berms and traps), and (2) leadassociated with ash from burnedmunitions that was reportedly spreadover 10 acres (exact locations have notbeen identified). Other sources mayinclude: (3) lead from historical exhaustdeposited by car, truck and aircraftusing leaded fuels and oil, and (4) leadassociated with buried unexplodedordnance including small rounds andprimary metallic explosives (lead).Lead contamination needs to beaddressed at other firing ranges in theYellow Water Weapons Area.
Sampling Techniques and SamplingData
Lead poses the greatest potential hazardbecause it has been found in all mediasampled (soil, surface water, sediment,groundwater) and in very highconcentrations, except in groundwater.The reported median lead level in soil is163 parts per million (ppm), theaverage is 1,157 ppm, and themaximum level found was 65,500 ppm.
The lead levels reported are a composite (mixture) of soil taken between the surface and one foot below the surface. Since lead tends to accumulate in the soil surface, usually within 1 to 2 inches of the surface, and concentrations decrease with depth (U.S. EPA, 2001), this method mixes contaminated soil with uncontaminated soil from the surface to one foot depths. Therefore, the reported lead concentrations and associated statistical averages are less than the levels that would be found at the surface at each sampling location. For example, the surface levels may be as much as 15 times higher than current sampling results show including statical averages.(1)
Similarly, at a shooting range like the one at NAS Cecil Field, 91% of shot is found in the top one inch of soil at a trap and skeet range (Vyas, 2000). Therefore, the surface concentrations at the shooting range may also have higher averages.
Figure 9 shows the sampling locations. We suggest that interested readers get a copy of the Navy's electronic version of this document to view the contaminant trends and concentrations at each location on Site 15.
The current preliminary sampling data provides information on the general trend of (diluted) lead contamination. However, additional sampling to determine the range of dilution would be needed if people, especially children, would be in contact with soils at Site 15 on a more frequent basis (i.e., several times a week). If the range of dilution can be determined by a focused sampling plan (e.g., using an X-Ray Fluorescence (XRF) machine in combination with confirmation sampling), then a dilution factor could be used to better estimate the lead concentration that people would come in contact with. That information could then be used to generate a map identifying soil concentration trends and areas with different contamination histories which may have a different bioavailability potential. For this trend map, surface soil should be defined as the top 0-3 or 0-6 inches of soil. If the surface is grassed covered, surface soil is considered the 2 inches below the grass layer (U.S. EPA, 1992a).
Future Land Use
The Base Reuse Plan for NAS Cecil Field envisions a wildlife corridor that will extend along the western edge of the base, from the south (Main Base area) to the north (YWWA), and incorporating Site 15. Future activities within the wildlife corridor may include forest management and recreational uses such as horseback riding, biking, and hiking (Arthur Andersen LLP, 1996).
The current record of decision on the cleanup remedy is yet unsigned as of this document release. If changes in the economy or regional vision for NAS Cecil Field redevelopment result in a proposed residential reuse or recreational activities where children could have frequent (i.e., several times a week) contact with the soils, and in the absence of soil clean-up or information on the bioavailability of the lead, future recreational or residential exposure to the Site 15 surface soils poses an unacceptable health hazard.
Public Health Implications
Children who, in the future, may play on the unremediated parts of Site 15 in the Yellow Water Weapons Area (YWWA) may be exposed to lead in soil at levels that may result in adverse health effects. The perimeter of the YWWA is fenced but untended. The community has open access to most of this area. Sites 14 (Blue 5 Ordnance Disposal) and 15 (Blue 10 Ordnance Disposal) are located in relatively remote, interior areas of YWWA, are heavily wooded, and posted with no trespassing signs. It is not likely that children and youth will come into contact with contaminants in these areas prior to completion of investigation and clean-up activities by the base. However, left unremediated, routine contact (i.e., several times a week) with soil at Site 15 may increase blood lead levels, especially in children, to unsafe levels.The lead sampling method of combining higher lead contaminated soil with uncontaminated soil under estimates potential exposures to lead. However even these diluted concentrations are of public health concern for those coming in contact with lead contamination.
The median lead levels (actual media would be higher when adjusted for dilution) in soil (at unspecified depths) were 163 ppm with maximum levels as high as 65,500 ppm. Calculated increases in blood lead levels ranged from 8 to 34 µg/dL. Adding these values to the baseline blood lead concentrations for U.S. children, one arrives at predicted blood lead levels ranging from approximately 11 to 38 µg/dL for children exposed daily to the soils at Site 15. Therefore, the predicted exposures could possibly result in increases in blood lead levels which exceed the 10 µg/dL screening criterion. The algorithm, soil lead data, assumptions, and calculations are provided in Appendix G.
CDC recommends that all children be screened for lead poisoning at least annually, especially children between the ages of 6 months and 6 years of age (CDC, 1991a). Young children and children exposed in utero are most vulnerable to lead toxicity for several reasons, including: (1) greater absorption and metabolism of lead than adults, (2) rapidly developing nervous systems, and (3) for children, higher intakes of air, food, and water on a body weight basis. In addition, children age 3 and under tend to chew and mouth their hands, toys, and other objects, exposing them to lead dusts and paints (CDC, 1991a). Blood lead levels of 10-40 micrograms per deciliter (µg/dL) may not cause distinctive symptoms of lead poisoning, but are associated with impaired central nervous system development, lower IQs, and hearing problems in children (CDC, 1991a; ATSDR, 1999a).
The groundwater at Site 15 has been shown to have antimony and lead contamination at levels of health concern. Currently, groundwater is not used as drinking water in the vicinity. Future changes in the base reuse plan should restrict the installation of potable water wells at, or downgradient of, Site 15 without water treatment.
Unexploded ordnance (UXO) at Site 15 is likely left over from the firing range and would be smaller, less powerful rounds that would require lots of force to cause them to explode. However, one 500-pound general purpose high explosive blast and fragmentation bomb was found and removed. Reportedly, only a visual inspection for other UXO was conducted. Therefore, digging or excavating in the area could be hazardous if the area is not cleared first. Reporting and clearing procedures need to be in place if future use includes any digging, clearing, and excavation. See the UXO section for reporting and clearing procedures.
- People who may eat fish or turtles from Yellow Water or Sal Taylor Creek draining Site 15
High dissolved lead levels (a median of 205 parts per billion (ppb)) have been found in surfacewater samples that run off Site 15. Dissolved lead means the lead is much more bioavailable andcan accumulate easily in fish and other wildlife. Bioconcentration levels of lead are above thebioaccumulation factor of 1,000 (U.S. EPA, 1999). During high water events, Yellow WaterCreek drains portions of Site 15 then flows into Sal Taylor Creek. Yellow Water and Sal Taylor Creek could be used for recreation and fishing.
Because there is soluble lead in drainage areas of Site 15, ATSDR recommended that the Navyin conjunction with state or local health and environmental agencies determine if fish and turtlesampling was necessary. In response, the Navy modeled lead contamination in fish and predicteda very low (<0.01 mg/day) average daily intake for people eating fish from this area. It is stillunknown whether people are harvesting fish and turtles from this area, but it seems unlikely thatthey would be harvesting it frequently (daily). Therefore, currently, this situation poses noapparent public health hazard.
If Site 15 soils are left unremediated, more soluble lead and possibly other metals could enter drainage areas. If more people use this area for the recreational harvesting of fish or turtles from Yellow Water or Sal Taylor Creek, ATSDR recommends sampling surface water, sediments, fish, and aquatic animals in Yellow Water and Sal Taylor Creek and other creeks downstream from Site 15 for metals (especially lead and mercury), PAHs and pesticides. This possibility should be evaluated as part of the Superfund Comprehensive Five Year Review.
PUBLIC HEALTH ACTION PLAN- SITE 15 AND OTHER AREAS OF THE YWWA
People contacting on-site soil, dust, creeks, groundwater, and unexploded ordnance
People who eat fish or turtles from Yellow Water or Sal Taylor Creek draining Site 15
ACTIONS TAKEN OR PLANNED
Contact with soils
Eating locally caught fish and turtles
Contact with Unexploded Ordnance
Use of Groundwater
1. Assume that all of the contamination is in the top 2 cm and the samples were takes at 0-30 cm (30 cm = 12 inches). 30 cm is 15, 2 cm intervals. For simplicity, assume a total concentration of 10 ppm, then (X ppm + 0 ppm)/15 = 10 ppm. X=150, therefore, the top 2 cm is 15 times the average over 30 cm.